High-energy propellant



'5, 1969 J. E. PAUSTIAN ETAL 3,459,607

HIGH-ENERGY PROPELLANT Filed May 12, 1966 INERT GAS INVENTORS JOHN f. PAUST/AN MAAV/N M. FE/N nrrokusr United States Patent 3,459,607 HIGH-ENERGY PROPELLANT John E. Paustian, Whippany, and Marvin M. Fein, Westfield, N.J., assignors to Thiokol Chemical Corp., Bristol, Pa. a cor oration of Delaware Fi led May 12, 1966, Ser. No. 551,838

Int. Cl. C06b 19/02 US. Cl. 1498 6 Claims ABSTRACT OF THE DISCLOSURE Hydrazinium azide propellants are disclosed having a novel form rendering them useful in guns and the l ke. In addition, these propellants are coated with burning rate control materials. Methods for making these propellants, which comprise forming the propellant material in sphericall shaped particles and thereafter coating the particles with a burning rate control material, are also included.

This invention relates to a high-energy propellant and more particularly to a propellant that can advantageously be used for propelling projectiles to high velocities.

Heretofore, hydrazinium azide has been utilized as a gun propellant in loose powder and pressed pellet forms. In such forms, however, hydrazinium azide propellants are not completely satisfactory from the standpoint of control and reproducibility of their burning rates. Furthermore, the burning characteristics of the aforesaid types of hydrazinium azide gun propellants are such that the pressure produced in a gun barrel in which the propellants are used is initially high but rapidly decreases before a projectile propelled thereby reaches the muzzle of the gun barrel. As will be understood by persons skilled in the art of gun propellants, the barrel pressure produced by hydrazinium azide gun propellants preferably should be relatively constant throughout the travel of a projectile in a gun barrel. In addition, previously available hydrazinium azide propellants undergo a considerable decrease in efficacy when they are exposed, even for a relatively short period, to moist environments.

It is accordingly a broad object of this invention to provide an improved hydrazinium azide product which can advantageously be used as a gun propellant, as well as for other purposes.

Another object of this invention is to provide an eflicient method of producing an improved hydrazinium azide product.

Still another object of this invention is to provide a hydrazinium azide gun propellant that produces a relatively constant barrel pressure in a gun in which it is employed.

An additional object of this invention is to provide a hydrazinium azide product having burning characteristics that make it a more effective gun propellant than known hydrazinium azide gun propellants.

A further object of this invention is to provide a hydrazinium azide gun propellant that is less susceptible to deterioration, when exposed to a moist environment, than the hydrazinium azide gun propellants heretofore available.

Briefly described, hydrazinium azide propellants in accordance with the present invention are prepared by: (l) melting hydrazinium azide and dropping it into a column of liquid which has a density only slightly less than that of said hydrazinium azide and which has a heated upper stratum and a cooled lower stratum, thereby forming solid globules of the hydrazinium azide; (2) contacting these globules with a solution comprising a non-aqueous vehicle and a coating material having a burning rate lower than that of said hydrazinium azide, so as to thereby cover the surface of each of said globules with the vehicle-coating material solution; and (3) thereafter contacting the solution-covered globules with an extraction liquid in which the non-aqueous vehicle is soluble and in which the coating material is insoluble, so as to thereby transfer the non-aqueous vehicle from the surfaces of the hydrazinium azide globules to the aforesaid extraction liquid while leaving the coating material on said globules.

The novel features of the present invention, as well as additional objects and advantages thereof, will be more clearly understood from the following description, in which reference is made to the accompanying schematic representation of apparatus that can advantageously be used in producing hydrazinium azide propellant in accordance with the invention.

Throughout the specification and drawing, the same numbers designate the same or corresponding parts.

In the accompanying drawing the number 10 generally designates one apparatus that can be employed in carrying out a process embodiment of this invention. More particularly, apparatus 10 comprises a vertical, closed tubular column 12 the lower end of which is fixedly attached to, and in communication with the interior 14 of, a frustoconical vessel 16. The lower end of vessel 16 is open and formed with a circumferentially extending, laterally projecting flange 18 to which is detachably connected a disk-shaped closure member 20. Fixedly joined to, and depending from, closure member 20 is a discharge conduit 22 the upper end of which communicates with an aperture in said closure member (and thus with the interior 14 of vessel 16 when the closure member is attached to flange 18 as illustrated). Connected to vessel 16 is a conduit 24 in which there is a valve 26 that can be opened to fill the vessel and column 12 with a liquid 28 to be described hereinafter. Conduit 22 is provided with a valve 30 that can be opened to draw off this liquid as desired. A wire screen 31 is positioned over conduit 22 to retain the hydrazinium azide product 32 produced in apparatus 10 and collected in vessel 16.

Disposed around the lower portion of column 12 is a heat exchanger 34 having an inlet 36 and outlet 38. A reflux column 40 extends obliquely from the upper end of column 12 and communicates with the interior of the latter and with a duct 42, this reflux column passing through an aperture 44 formed in the side wall 46 of a closed cylindrical member (generally designated by the number 48) the lower end of which is positioned around the upper portion of column 12. More specifically, member 48 is provided with an apertured partition 50 and with end plate 52, 54 so that its interior is divided into an upper chamber 56 and lower chamber 58, each of said chambers having an inlet 60, 62 and an outlet 64, 66. End plate 52 is formed with a centrally disposed aperture 68 in which a dropping funnel 70 is sealably engaged, this funnel having a lower portion 72 of lesser diameter which extends through the aperture in partition 50, and which is provided with a valve 74 adapted to be actuated from a point outside apparatus 10. The lower portion 72 of dropping funnel 70 also extends through an aperture in the end closure of column 12 to a point below the junction of reflux column 40 with said column 12. Extending laterally from the upper portion of dropping funnel 70 is a charging chute 76 the opening of which can be sealed by a detachable lid 78. A duct 79 communicatively connects duct 42 with the interior 82 of dropping funnel 70. Disposed around reflux column 40 is heat exchanger 86 having an inlet 88 and an outlet 90.

It will be recognized that the above-described components of apparatus 10 may be formed of many different Well-known materials, such as, for example, glass or suitable metals.

In accordance with a preferred method embodiment of this invention, column 12 and vessel 16 are filled with 1,2-dichloroethane, the surface level of this liquid being maintained at a point above the end of portion 72 of dropping funnel 70 and below the junction of reflux column 40 with column 12. With valve 74 closed, solid hydrazinium azide is charged into the larger upper portion of dropping funnel 70 through chute 76 and the dropping funnel is sealed by securing lid 78 to the top of said chute. A suitable hot liquid is then pumped through inlet 60 into the annular space between dropping funnel 70 and member 48 and out through outlet 64. Simultaneously an inert gas such as nitrogen is forced, substantially at atmospheric pressure, through duct 42 in the direction indicated by the arrow in the drawing. The temperature of the hot liquid injected into inlet 60 is slightly higher than the melting point of hydrazinium azide, or above about 75 C. A suitable hot liquid is also pumped through inlet 62 into the annular space between the upper end of column 12 and member 48 and out through outlet 66 (the temperature of this liquid preferably being such that the upper stratum of the 1,2-dichloroethane in column 12 is maintained at about 80 C.), and a suitable coolant is pumped through inlet 36 into the annular space between the lower end of column 12 and the wall of heat exchanger 34 and out through outlet 38 (the temperature of this coolant being such that the 1,2-dichloroethane in the lower portion of column 14 is maintained at a temperature of about l C. to about l0 C.). The temperature of the upper end of reflux column 40 is maintained at about 15 C. by pumping a suitable coolant through heat exchanger 86 After the hydrazinium azide in dropping funnel 70 has been melted, valve 74 is opened to permit dropwise flow of the hot hydrazinium azide through the orifice in the lower portion 72 of said dropping funnel and into the heated upper stratum of the l,2-dichloroethane in column 12. Because the density (1.25 gm./cc.) of 1,2-dichloroethane is only slightly less than that (1.38 gm./cc.) of hydrazinium azide, each drop of the latter settles slowly toward vessel 16 and is gradually cooled. After passing through the stratum of the 1,2-dichloroethane which is at a temperature of about --15 C. to about C., each drop of hydrazinium azide is solidified into a spherical solid particle.

-It will be noted that the inert gas forced through duct 42 not only enters the space above the hydrazinium azide in dropping funnel 70 but also enters reflux column 40. Thus the design of apparatus 10 minimizes the possibility of ignition of any combustible vapors in dropping funnel 70, reflux column 40 and the upper end of column 12.

The dimensions of certain components of apparatus 10 will vary depending upon the size of the globules of hydrazinium azide that it is desired to produce. For example, the diameter of the orifice in the lower portion 72 of dropping funnel 70 may be made relatively large in order to introduce large drops of the melted hydrazinium azide into the 1,2-dichloroethane in column 12, and to thereby produce a product in the form of relatively large globules. Conversely, smaller globules of hydrazinium azide can be formed by use of a small orifice in the lower portion of dropping funnel 70. It has been found that well-formed globules having a diameter between about 0.075 inch and 0.125 inch are produced in apparatus of the type described and illustrated, wherein the diameter of the orifice in the lower portion 72 of dropping funnel is 0.023 inch and the distance between the end of said portion 72 and the bottom of vessel 16 is in the range of about 18-24 inches.

After a quantity of hyraziniurn azide globules has been collected in vessel 16 the valve 30 to is h rge cond it 2 .4 is opened to drain the 1,2-dichloroethane from said vessel and column 12. Closure member 20 is then detached from vessel 16 and the hydrazinium azide globules are screened to separate them into different size ranges. The hydrazinium azide globules obtained by the above-described process and apparatus can be dried by conventional techniques and then utilized as a high-energy gun propellant for hypervelocity applications. However, in accordance with the principles of this invention, the globules of a selected size range (which will vary according to the intended use of the propellant) are preferably coated with a coating material that will modify the burning characteristics of the globules and also protect them from moisture absorption. This coating preferably is applied to the globules by mixing them with a solution consisting of: 1) about 1 to 10 percent by weight of a coating material, preferably nitrocellulose, which has a burning rate lower than that of hydrazinium azide and which will also protect said hydrazinium azide from moisture absorption; and (2) a non-aqueous vehicle, preferably ethyl acetate, which is soluble (or miscible) with a second liquid that will be described hereinafter. Although the hydrazinium azide globules can readily be coated with the aforedescribed non-aqueous vehicle-coating material solution by mixing the materials in a suitable vessel, it will be obvious that other means can be employed to cover the globules with this solution, such as, for example, conventional spraying apparatus. It has been found preferable to mix the hydrazinium azide globules with a lacquer consisting of about 2.5 percent by weight nitrocellulose and about 97.5 percent by weight of ethyl acetate, mixing being effected at atmospheric temperature and pressure in a conventional blending machine and with a ratio of 1 gm. of hydrazinium azide globules per 2.5 ml. of the nitrocellulose-ethyl acetate solution. After the globules have been thoroughly mixed with a selected non-aqueous vehiclecoating material solution, the resulting slurry is mixed with an extraction liquid in which the non-aqueous vehicle is soluble and in which the selected coating material is insoluble. In the preferred embodiment of the invention herein described, the slurry of hydrazinium azide globules and nitrocellulose-ethyl acetate solution is slowly added to a liquid consisting of about 75 percent by volume of 1,2-dichloroethane and 25 percent by volume of carbon tetrachloride, and this mixture is agitated for approximately 15 minutes at atmospheric pressure and temperature, which transfers the ethyl acetate (the non-aqueous vehicle used in the preferred process) from the surfaces of the hydrazinium azide globules while leaving the nitrocellulose (the coating material used in the preferred process) on the surfaces of said globules. The slurry of hydrazinium azide globules and nitrocellulose-ethyl acetate solution is combined with the mixture of 1,2-dichloroethane and carbon tetrachloride in the ratio of 6.25 ml. of the latter per each gram of hydrazinium azide globules in the slurry. The 1,2-dichloroethane-carbon tetrachloride mixture is particularly advantageous as the extraction liquid because of its miscibility with ethyl acetate, its non-flammability, and the insolubility of both hydrazinium azide and mitrocellulose in said mixture. Also the density of the mixture of the slurry and extraction liquid is such that the hydrazinium azide globules coated with the nitrocellulose-ethyl acetate lacquer are suspended in the mixture, whereas the globules which are coated only with nitrocellulose (i.e., the globules from whose lacquercovered surfaces the ethyl acetate has been extracted) sink, thereby minimizing agglomeration of the nitrocellulose-coated globules and lacquer-coated globules. Agitation of the mixture is continued until the ethyl acetate in the lacquer on the hydrazinium azide globules has been completely extracted.

After the nitrocellulose-coated globules of hydrazinium azide have been separated from the aforedescribed mixture of extraction liquid and non-aqueous vehicle (which Peak Propellant barrel Muzzle weight pressure velocity Propellant (grains) (p.s.i.) (f.p.s.)

Hydrazinium azide globules (uncoated, size range 0075-0125 inch)- 45. 1 20, 500 6, 531

D0 67. 5 73, 500 8, 792 Hydrazinium azide globules (nitrocellulose-coated, size range 0.075-

0.125 inch) 60. 0 60, 200 8, 531

A particular advantage of the disclosed process for preparing hydrazinium azide propellant is that the hydrazinium azide particles produced thereby are uniformly spherical in shape, which simplifies the preparation of a propellant having controlled, reproducible and uniform burning characteristics. The disclosed process can also readily be adapted to produce hydrazinium azide globules of difierent sizes, which can be selectively blended to provide propellants of different burning characteristics.

The nitrocellulose-coated globular hydrazinium azide propellant of this invention is particularly advantageous as a gun propellant as it produces a relatively constant pressure in a gun barrel throughout the travel of a projectile therein. Furthermore, the nitrocellulose coating on each hydrazinium azide globule is uniformly applied by the coating process herein disclosed and serves to protect the hydrazinium azide from moisture absorption and adsorption. The scope of this invention is not limited, however, to a globular hydrazinium azide propellant that is coated, or to the same propellant coated with nitrocellulose. It will be apparent to those skilled in the art that other embodiments, as well as modifications to those disclosed, can be made and practiced without departing from the scope of the invention, for the limits of which reference must be made to the appended claims.

What is claimed is:

1. A method of preparing a propellant comprising the steps of:

forming hydrazinium azide into substantially spherical solid particles;

contacting said particles with a solution comprising a non-hygroscopic coating material having a burning rate lower than that of said hydrazinium azide and a non-aqueous vehicle for said coating material, so as to thereby cover the surfaces of said particles with said solution;

contacting said solution-covered particles with an extraction liquid in which said non-aqueous vehicle is soluble and in which said coating material is insoluble, so as to thereby transfer said non-aqueous vehicle from the surfaces of said particles to said extraction liquid while leaving said coating material on said particles; and separating said extraction liquid and non-aqueous vehicle therein from said particles and thereafter drying the latter. 2. The method of claim 1 wherein said coating material is nitrocellulose.

3. The method of claim 1 wherein said spherical particles of hydrazinium azide are formed by the steps of:

heating said hydrazinium azide under an inert atmosphere to thereby bring it to a fluid state; and dropping said fluid hydrazinium azide into an inert liquid an upper stratum of which is at a temperature above about 80 C. and a lower stratum of which is at a temperature of about 15 C. to about 10 C., so as to solidify said fluid hydrazinium azide in substantially spherical form. 4. The method of claim 2 wherein said inert liquid is 1,2-dichloroethane.

5. A method of preparing a propellant comprising the steps of:

forming hydrazinium azide into substantially spherical particles; immersing said particles in a lacquer comprising from about 1 to about 10 percent by weight of nitrocellulose and from about 90 to about 99 percent by weight of ethyl acetate, so as to thereby form a slurry of said lacquer and particles; admixing said slurry with an extraction liquid comprising about percent by volume of 1,2-dichloroethane and 25 percent by volume of carbon tetrachloride; and separating said extraction liquid and ethyl acetate therein from said particles and thereafter drying the latter. 6. The method of claim 5 wherein said spherical particles of hydrazinium azide are formed by the steps of: heating said hydrazinium azide under an inert atmosphere to thereby bring it to a fluid state; and dropping said fluid hydrazinium azide into 1,24lichloroethane an upper stratum of which is at a temperature above about C. and a lower stratum of which is at a temperature of about 15 C. to about 10 C., so as to solidify said fluid hydrazinium azide in substantially spherical form.

References Cited UNITED STATES PATENTS 2,398,071 4/1946 Barab 149-8 X 2,615,800 10/1952 Goodale 149-8 3,194,851 7/1965 Sauer et a1. 264-3 CARL D. QUARFORTH, Primary Examiner MELVIN I. SCOLNICK, Assistant Examiner U.S. Cl. X.R. 14936, 94;--264--3 

